While playing Dodgeball in the gym, you can stop the game by pressing the L2 button (Help) during the time the game is stopped no hits will be counted. So to use this in your favour, move as far away from the person with the ball, wait till the ball gets thrown, and hit L2. The ball will hit you but it won't count; then just pick it up and do the jumpshot and you will be winning in no time!